Stone — Granitic Breccias of the Cripple Greek Region. 29 



the grits found at dike !No. 4 between granite walls. I con- 

 sider them as granitic breccias composed of dike ejectamenta. 



9. Phonolite and rhyolite dikes on Grouse Mt. Elevation of 

 grits from 9100 up to' 9800 feet. 



This mountain contains very large dikes of both rhyolite and 

 phonolite and both kinds of dikes are capped and bordered by 

 granitic grits. When the grits cap a phonolite dike they con- 

 tain some fragments of phonolite ; when they cap a rhyolite 

 dike they contain fragments of rhyolite. This is- strongly 

 against the sedimentary theory of the origin of these grits, 

 which I regard as granitic breccias like the rest. 



10. Phonolite dike on Beacon Hill. 



At various points along the western slopes of this hill are 

 found granitic grits indistinguishable from the grits on Grouse 

 and Straub Mountains. If the latter are lake beds, so are these 

 on Beacon Hill. Elevation of the grits about 9500 feet. 



11. Andesite dike on the top of Mineral Hill. Elevation 

 10,150 feet. 



The extreme top of this hill consists of a firm grit composed 

 almost wholly of granite but with an admixture of andesite. 

 The fragments are rather more angular than at the other dikes 

 here described. Going down in shafts, we find an increasing 

 proportion of andesite. So also as we go down the surface 

 slopes of the hill we find more and more andesite till we soon 

 reach the characteristic andesitic breccia. 



The granitic grit on the top of Mineral Hill is plainly a 

 breccia like the more andesitic breccia that underlies it, and 

 they pass into each other by insensible gradations. We can- 

 not account for the granitic fragments as explosive ejectamenta 

 in such a position, but they can easily be accounted for as dike 

 ejectamenta if we suppose they were cemented immediately 

 after being raised above the original surface. This would pre- 

 serve the continuity of the granitic gravel as a cap and the 

 andesitic fragments pushed up subsequently as a body of loose 

 gravel would spread laterally underneath the cap and gradually 

 be cemented to it. 



12. Andesite dike on the ]N". W. Spur of Khyolite Mountain. 

 Elevation 9900 feet. 



Here some mining shafts penetrate an andesitic breccia that 

 is so weakly cemented as soon to fall to pieces after being 

 exposed to the weather. They next pass through a stratum of 

 well-rounded granitic gravel, pebbles and cobbles, and then 

 into the granite. These stones have the same shapes as those 

 at the Cripple Creek reservoir. The most probable interpreta- 

 tion is as follows : 



The andesite dike was slowly rising through the granite and 

 as it did so it pushed a mass of granite before it, crushing it in 



